Resilient Packet Ring, hereinafter referred to as RPR, is a new technique of Medium Access Control (MAC) layer, which is being standardized by IEEE802.17 workgroup. This new layer 2 link technique can perform service transmission based on any kind of physical layers, such as Ethernet, Synchronous Digital Hierarchy/Synchronous Optical Network (SDH/SONET), Dense Wavelength Division Multiplexing (DWDM) and so on. The RPR technique is used to construct a metropolitan area network centered on data on the basis of ring topology, and it can provide data-optimized bandwidth management and solution for highly cost-effective multi-service transport, as well as provide a relatively sophisticated protection switching mechanism. As shown in FIG. 1, a dual-fiber structure is adopted by the RPR network, and each fiber can transmit both data services and control information. An RPR node is composed of one physical layer entity and one MAC sub-layer entity. A MAC layer client may transmit data services by one ringlet, and transmit control information by the other ringlet. In this way, data can be transported upon two fibers at the same time by the RPR technique, thus it can accelerate transmission of control information, and realize bandwidth adaptation and fast self-cure.
Compared with the prior art, the RPR technique provides many advantages, e.g., the RPR can increase bandwidth utilization ratio, equally allocate bandwidths among nodes, as well as support plug and play, and various priority services.
The resiliency of RPR means the ability to implement protection switching, i.e., services can be automatically protected by switching within 50 ms when a fault occurs in a closed-ring and be recovered when the fault is gone. There are two protection switching modes defined in the RPR protocol, one is a Steering mode based on a new topology structure, and the other is a Wrapping mode which requires two nodes on both sides of a fault to carry out switching. The Steering mode is a default protection approach of the RPR network, which is supported by all nodes in the network according to protocols. That is, the Steering mode is mandatory, while the Wrapping mode is optional. It is well known by those skilled in the art that trigger conditions of protection switching include line invalidation, node invalidation, service degradation, imperative switching, and so on.
As shown in FIG. 2, for the Steering mode, Station1 . . . Station6 represent 6 network nodes, the inner ringlet and the outer ringlet of RPR are expressed as Inner Ringlet and Outer Ringlet respectively, the fault between Station5 and Station6 is denoted as Fiber Cut (FC), and the dotted line in FIG. 2 denotes transmission path of outer ringlet data after switching. When the network detects a fault, wrapping protection may not be carried out at the two nodes adjacent to the fault, and topology search is performed at once, thus route is optimized according to a new topology structure. Then, the source node may directly transmit data to the destination node according to the new topology path. Namely, if the path between Station5 and Station6 is broken down, the information is broadcast in the RPR network. Then, the source node Station4 will change to inner ringlet to transmit data after receiving this information, and the data will be sent to the destination node Station1 via Station3 and Station 2. During the procedure, a small portion of data already sent out from the source node will be discarded at the fault node.
As shown in FIG. 3, for the Wrapping mode, Station1 . . . Station6 represent 6 network nodes, the inner ringlet and the outer ringlet of RPR are expressed as Inner Ringlet and Outer Ringlet respectively, the fault between Station5 and Station6 is denoted as Fiber Cut (FC), and the dotted line in FIG. 3 denotes transmission path of outer ringlet data after switching. When a node detects a fault initiating the switching, adjacent nodes of the fault will be switched, and protection information will be broadcast to other nodes in the RPR network. Then, data will be sent to the destination node through a switched path of the node, that is, data stream from outer ringlet enters inner ringlet at Station5, and continues to be transmitted after circling the inner ringlet once.
Although the Wrapping mode forwarded by IEEE802.17 workgroup is a fast way without data loss, there is not any specific technical scheme to implement Wrapping mode yet. Therefore, a method is needed to implement Wrapping mode in an RPR network.